I know that Δ9-tetrahydrocannabinol and other cannabinoids increase dopaminergic neurotransmission in the nucleus accumbens and that this is what results in the euphoria experienced by cannabis users. Other than this I do not know what effect cannabinoids have on monoaminergic neurotransmission. I would assume that it increases monoaminergic neurotransmission seeing how rimonabant $-$ a selective CB1 inverse agonist $-$ leads to depression and anxiety which according to the monoamine hypothesis can likely be linked to changes in the activity of monoaminergic pathways in the brain.